Normally, a tilt mechanism that makes it possible to adjust the height position of the steering wheel, and a telescopic mechanism that makes it possible to adjust the forward-backward position of the steering wheel according to the size and driving posture of the driver are assembled in the steering apparatus of an automobile. Moreover, assembling an electric power steering apparatus that uses an electric motor as a power source and that is able to reduce the force necessary for the operator to operate the steering wheel is also widely performed. FIG. 25 illustrates a conventional example of an electric power steering apparatus that comprises a tilt mechanism and a telescopic mechanism.
The steering apparatus comprises: a steering shaft 2 to which a steering wheel 1 is fastened to the rear end section thereof, a steering column 3 that supports the steering shaft 2 on the inside thereof so as to be able to rotate freely, an electric assist apparatus 4 for applying an assist torque to the steering shaft 2, and a steering gear unit 6 for pushing or pulling a pair of left and right tie rods 5 according to the rotation of the steering shaft 2. In this specification, the forward-backward direction is the forward-backward direction of the vehicle body.
In an electric power steering apparatus, the steering shaft 2 is constructed so as to be able to expand and contract in the axial direction by combining an inner shaft 7 that is located on the front side and an outer shaft 8 that is located on the rear side such that torque can be transmitted and such that relative displacement in the axial direction is possible. Moreover, the steering column 3 is constructed so as to be able to expand and contract in the axial direction by combining an inner column 9 that is located on the front side and an outer column 10 that is located on the rear side such that relative displacement in the axial direction is possible. The outer shaft 8 is supported on the inside of the outer column 10 such that displacement in the axial direction with respect to the outer column 10 is suppressed, and so as to be able to rotate freely.
The front end section of the inner column 9 is connected and fastened to the rear end surface of a housing 11 of the electric assist apparatus 4. On the other hand, the inner shaft 7 is inserted inside the housing 11, and the front end section thereof is connected to the input shaft of the electric assist apparatus 4. Moreover, the front end section of the output shaft 12 of the electric assist apparatus 4, which is connected to the input shaft by way of a torsion bar, protrudes from the front end surface of the housing 11 and is connected to the input shaft 21 of the steering gear unit 6 by way of a universal joint 18, and intermediate shaft 19 and another universal joint 20.
The inner column 9 is supported by a front support bracket 13 by part of the vehicle body 14 by way of the housing 11. In order to achieve the tilt mechanism, the front support bracket 13 supports the housing 11 so as to be able to pivot freely around a tilt pivot shaft 15 that extends in the width direction of the vehicle body 14 (front-back direction in FIG. 25) and that is supported by the front support bracket 13.
The middle section of the outer column 10 is supported by a rear support bracket 16 by part of the vehicle body 14. In order to achieve the tilt mechanism and the telescopic mechanism, the outer column 10 is supported by the rear support bracket 16 so as to be able to be switched between a fixed state, in which movement in the forward-backward direction and movement in the up-down direction is not possible, and a non-fixed state, in which movement in the forward-backward direction and movement in the up-down direction is possible. In regards to this kind of support construction, various kinds of construction are known and are not the features of the present invention, so the detailed explanation is omitted.
In the case of this kind of electric power steering apparatus, when adjusting the height position and forward-backward position of the steering wheel 1, by rotating an adjustment handle 17 (see FIG. 26) in a specified direction (normally downward), the middle section of the outer column 10 is set in the non-fixed state with respect to the rear support bracket 16. Then, in this state, the height position of the steering wheel 1 is adjusted by pivoting the steering column 3 around the tilt pivot shaft 15. Moreover, the forward-backward position of the steering wheel 1 is adjusted by expanding or contracting the steering column 3 and steering shaft 2. After adjustment, by rotating the adjustment handle 17 in a direction opposite the specified direction (normally upward), the middle section of the outer column 10 is set in the fixed state with respect to the rear support bracket 16.
Moreover, the electric assist apparatus 4 is constructed such that when a torque is applied to the steering shaft 2 from the steering wheel 1 during steering, the direction and size of the torque is detected by a torque sensor that is provided inside the housing 11, and according to the detected torque, an electric motor 22 that is supported by the outer surface of the housing 11 applies an assist torque (assist force) to the output shaft 12 by way of a worm reducer that is provided on the inside of the housing 11.
In an electric power steering apparatus that comprises this kind of position adjustment mechanism for a steering wheel 1, as disclosed in JP3707252 (B2), by assembling bushings in the sliding portion of the tilt pivoting portion, which is the portion around which the steering column 3 pivots, it is possible to improve the durability of this tilt pivoting portion. FIG. 26 to FIG. 31 illustrate a first example of conventional construction of a steering column support apparatus for an electric power steering apparatus in which bushings are assembled in the tilt pivoting portion.
The front support bracket 13a is made using a metal plate such as steel plate, and has a pair of parallel support plate sections 23 that are separated in the width direction of the vehicle body 14 (front-back direction in FIG. 26 and FIG. 30, and left-right direction in FIG. 27, FIG. 28 and FIG. 29). Moreover, the tilt pivot shaft 15a is located in the width direction of the vehicle body 14 so as to be spanned between the bottom portions near the bottom ends of the pair of support plate sections 23. The tilt pivot shaft 15a is composed of a tilt bolt 24 that is made of a metal material such as steel, and a cylindrical sleeve 25 that is made of a metal material such as steel, aluminum alloy or the like. The tilt bolt 24 is installed so as to be spanned between the support plate sections 23 by inserting the rod section thereof through a pair of circular holes 26 that are concentrically formed in portions near the bottom ends of the pair of support plate sections 23, then screwing a nut 27 on a male screw section that is formed on the tip end section of the rod section, and by tightening. Furthermore, the sleeve 25 is fitted around the outside of the rod section of the tilt bolt 24, and held and fastened between the support plate sections 23 by tightening the nut 27.
The housing 11a of the electric assist apparatus 4a is made of a metal material such as an aluminum alloy, and a pivot bracket 28 is integrally provided on the front end section thereof. A through hole 29 is formed in the tip end section of the pivot bracket 28 in the width direction of the vehicle body 14. The inner circumferential surface of the through hole 29 is composed of a stepped cylindrical surface wherein the inner-diameter dimension of both end sections in the axial direction is a little larger than the inner-diameter dimension of the middle section in the axial direction. Both end sections in the axial direction and the middle section in the axial direction of this stepped cylindrical surface are concentric with each other. The front end section to the middle section of the pivot bracket 28 is located between the support plate sections 23, and by supporting the pivot bracket 28 between the support plate sections 23 by way of tilt bolt 24 and sleeve 25 that are inserted through the through hole 29, the housing 11a and the steering column 3a are supported by the front support bracket 13a so as to be able to pivot around the tilt pivot shaft 15a. 
A pair of bushings 30 are fitted around the both end sections in the axial direction of the sleeve 25 of the tilt pivot shaft 15a. Each bushing 30 is formed into a tubular shape as a whole using an elastic material that includes a synthetic resin such as a polyamide resin, and an elastomer such as rubber or vinyl, or is formed using a low-friction material such as an oil impregnated metal, and comprises a cylindrical section 31; and a ring-shaped (outward facing flange section) side plate section 32 that extends outward in the radial direction from one end section in the axial direction of the cylindrical section 31. The cylindrical sections 31 of the bushings 30 are held between both end sections in the axial direction of the outer circumferential surface of the sleeve 25 and both end sections in the axial direction of the inner circumferential surface of the through hole 29 such that there is no loose movement in the radial direction. The side plate sections 32 of the bushings 30 are held between both side surfaces in the width direction of the pivot bracket 28 and the inside surface of the support plate sections 23 such that there is no loose movement in the axial direction.
In the case of this kind of conventional construction, the bushings 30 are attached to both end sections in the axial direction of the tilt pivot shaft 15a, so when adjusting the height position of the steering wheel 1, not only is direct rubbing between the tilt pivot shaft 15a and the pivot bracket 28 prevented even though the pivot bracket 28 pivots around the tilt pivot shaft 15a, but also direct rubbing between the support plate sections 23 and the pivot bracket 28 is prevented. Therefore, gaps in the tilt pivot portion that is composed of these members that are caused by advancing wear and plastic deformation due to direct rubbing between these members, which becomes the cause of looseness, is avoided.
In the case of an electric power steering apparatus, when the electric assist apparatus 4a applies an assist force to the output shaft 12a, the assist reaction force, which is the reaction force to the assist force, is applied to the housing 11a in the direction opposite the direction of rotation of the output shaft 12a. As a result, the pivot bracket 28 of the housing 11a receives the assist reaction force and tends to displace and incline in the direction opposite the direction of rotation of the output shaft 12a with respect to the tilt pivot shaft 15a and support plate sections 23. In doing so, the bushings 30 are elastically compressed between the tilt pivot shaft 15a and support plate sections 23 and the pivot bracket 28, or is pressed in the compressive direction, and by supporting the assist reaction force, suppresses displacement and inclination of the pivot bracket 28. As a result, direct rubbing between the pivot bracket 28 and the tilt shaft 15a and support plate sections 23 is prevented.
Incidentally, in the case of the first example of conventional construction, in order to maintain the support capability of the bushings 30 to support the assist reaction force, or in other words, in order to maintain the capability to suppress displacement and inclination of pivot bracket 28, the length in the axial direction of the cylindrical sections 31 and the height in the radial direction of the side plate sections 32 are increased somewhat. Moreover, the inside surfaces of the support plate sections 23 and both side surfaces of the pivot bracket 28, and both side surfaces of the side plate sections 32 are all parallel planes. Therefore, in the neutral state where the assist force is not generated, both side surfaces of the side plate sections 32, the inside surfaces of the support plate sections 23 and both side surfaces of the pivot bracket 28 are in contact over nearly the entire surface. Consequently, the contact surface area between both the inner and outer circumferential surfaces of the cylindrical sections 31 and the opposing surfaces (outer circumferential surface of the tilt pivot shaft 15a, or the inner circumferential surface of the through hole 29 of the pivot bracket 28), and the contact surface area between both side surfaces of the side plate sections 32 and the opposing surfaces (inside surfaces of the support plate sections 23, or both side surfaces of the pivot bracket 28) are increased by the amount that the length in the axial direction of the cylindrical sections 31, and the height in the radial direction of the side plate sections 32 are increased.
On the other hand, in the case of the first example of conventional construction, when adjusting the height position of the steering wheel 1, as the pivot bracket 28 pivots around the tilt pivot shaft 15a, sliding in the circumferential direction occurs at the contact area between at least one of the surfaces of the inner circumferential surfaces of the cylindrical sections and the outside surfaces of the side plate sections 32, and the outer circumferential surfaces of the cylindrical sections 31 and the inside surfaces of the side plate sections 32 of the bushings 30 and the opposing surface that faces this surface. The friction force that acts at this contact area becomes resistance when adjusting the height position of the steering wheel 1, so preferably this friction force is kept as low and stable as possible. However, because the contact surface area between both the inner and outer circumferential surfaces of the cylindrical section 31 and both side surfaces of the side plate sections 32 and the opposing surfaces are increased, the friction force that acts at the contact areas between the surfaces of the bushings 30 and the opposing surfaces is affected by the characteristics of these opposing surfaces, and becomes relatively high and unstable, so there is a possibility that the operational feeling when adjusting the height position of the steering wheel 1 will become bad.
On the other hand, FIG. 32A and FIG. 32B illustrate a second example and third example of conventional construction of a steering column support apparatus for an electric power steering apparatus as disclosed in JP2008-30728 A. In the construction of these examples, the inner circumferential surface of a through hole 29a that is formed in a pivot bracket 28a is caused to incline in a direction going away from the outer circumferential surfaces of cylindrical sections 31a of bushings 30a (30b) in going from the center section in the axial direction toward both end sections. As a result, cylindrical shaped gaps 33 having a wedge shaped cross section are formed in the portions on both sides of the center section in the axial direction between the inner circumferential surface of the through hole 29a and the outer circumferential surface of the cylindrical sections 31a. In the case of the second example of conventional construction illustrated in FIG. 32A, the outside surfaces of the side plate sections 32a of the bushings 30a are caused to incline in a direction going away from the inside surfaces of the of the support plate sections 23 in a direction outward in the radial direction. As a result, circular ring shaped gaps 34a having a wedge shaped cross section are formed between the outside surfaces of the side plate sections 32a and the inside surfaces of the support plate sections 23. On the other hand, in the case of the third example of conventional construction illustrated in FIG. 32B, the inside surfaces of the side plate sections 32b of the bushings 30b are caused to incline in a direction going away from the outside surfaces of the pivot bracket 28a in a direction outward in the radial direction. As a result, circular ring shaped gaps 34b having a wedge shaped cross section are formed between the inside surfaces of the side plate sections 32a and the outside surfaces of the pivot bracket 28a. Due to the existence of gaps 33, 34a, 34b that are formed in this way, the pivot bracket 28a (center axis of the through hole 29a) more easily inclines with respect to the center axis of the tilt pivot shaft 15a. 
Due to errors in the shape of the front support bracket 13a and the rear support bracket 16a, and due to an installation error when attaching the brackets to the vehicle body 14 (see FIG. 26), the guide direction in which the rear support bracket 16a guides the middle section of the steering column 3a during the tilting operating (see FIG. 26) may incline with respect to an imaginary plane that is orthogonal to the center axis of the tilt pivot shaft 15a. In the second and third examples of conventional construction, even in these cases, by the pivot bracket 28a inclining with respect to the center axis of the tilt pivot shaft 15a, the pivoting direction of the steering column 3a during height position adjustment of the steering wheel 1 (see FIG. 25), and the direction that the middle section of the steering column 3a is guided coincide with each other. Therefore, it is possible to avoid improper adjustment of height position of the steering wheel 1 due to discrepancy between the pivoting direction and the guide direction.
Furthermore, in the case of the second and third examples of conventional construction, the contact surface area between the inner circumferential surface of the through hole 29a and the outer circumferential surface of the cylindrical sections 31a decreases due to the existence of the gaps 34a, 34b. Therefore, it is possible to reduce the friction force that acts between the inner circumferential surface of the through hole 29a and the outer circumferential surface of the cylindrical sections 31a. Moreover, in the second example of conventional construction, it is possible to reduce the contact pressure between both side surfaces of the pivot bracket 28a and the inside surfaces of the side plate sections 32a, 32b (see FIG. 32A), and in the third example of conventional construction, it is possible to reduce the contact surface area between these areas (see FIG. 32B). Therefore, it is possible to stably reduce the friction forces that act between these surfaces, and by allowing slipping between the pivot bracket 28a and bushings 30a, 30b, it is possible to keep the resistance low when adjusting the height position of the steering wheel 1, and improve the workability of this height position adjustment.
However, in the case of the second and third examples of conventional construction, the support rigidity of supporting the pivot bracket 28a by the tilt pivot shaft 15a becomes low due to the existence of the gaps 33, and the support rigidity of supporting the steering wheel 1 (see FIG. 25) also becomes low. As a result, there is a possibility that the driver will have an uncomfortable feeling. Due to the assist reaction force that occurs during steering, the pivot bracket 28a inclines a relative large amount with respect to the center axis of the tilt pivot shaft 15a particularly due to the existence of gaps 33 of the gaps 33, 34a, 34b. Also due to this, there is a possibility that the driver will have an uncomfortable feeling.